Balanced inductance device



Feb. 7, 1933. A. J. CHRISTOPHER BALANCED INDUCTANCE DEVICE Filed June29, 1931 3 Sheets-Sheet l v /N VENTOR A .J. CHRISTOPHER A TTORNE' Y l933A. J. CHRISTOPHER 1,896,480

BALANCED INDUCTANCE DEVICE Filed June 29, 1931 3 Sheets-Sheet 2 //vVENTOR A .J. CHRISTOPHER ATTORNEY Feb. 7, 1933. A. J. CHRISTOPHERBALANCED INDUCTANCE DEVICE 3 Sheet-Sheet 3 Filed June 29. 1931 FIG. 6

i fl IN VEN TOR AJCHRISTOPHER ATTORNEY Patented Feb. 7, 1933 UNITEDSTATES BALANCED IN DUCTANCE DEVICE Application filed June 29,

This invention relates to inductance devices and more particularly tothose comprising a plurality of windings.

An object of theinvention is to provide an air core repeating coil ortransformer which has a low transmission loss and a low reflectioncoeflicient at frequencies within the so called carrier frequency range.

Another object of the invention is to provide an air core repeating coilor transformer which has a high degree of coupling between the primaryand secondary windings thereof, and at the same time an electrostaticshield between the windings to prevent the passage of noise orlongitudinal currents from the primary to the secondary winding.

Another object of the invention is to provide an air core repeating coilin which are combined the properties of voltage transformation and ofbroad band frequency selectivity.

A feature of the invention is a winding arrangement for a repeating coilor transformer in which two primary and two secondary windings areapplied partly as a quad and partly as individual twisted pairs.

Another feature comprises a winding arrangement in which the primarywinding or windings are placed inside of a hollow or cylindricalconductor or conductors and the secondary; winding or windings aretwisted with the hollow or cylindrical conductor or conductors.

Another feature of the invention is the proportioning of the number ofturns of the primary and secondary windings which are twisted together,and the number of turns of the primary and secondary windings which areseparately applied to secure the desired object.

The equivalent performance of a broad band pass filter can be obtainedin accordance with the invention by designing the air core repeatingcoil so that it has windings with proper self-impedance values, propercoupling coefficient between the primary and secondary windings and,when required, adding shunt capacities across the primary and secondarywindings. The theory of such an arrangement is the same as that givenin.

1931. Serial No. 547,618.

United States Patent No. 1,714,149, dated May 21, 1929, granted to H.Whittle and me, jointly.

The following formulae, the development of which was explained in theUnited States Patent No. 1,714,149, referred to above can be applied tothe design of repeating coils in accordance with this invention.

(1) Coefficient of coupling (5) Primary capacity W which is the minimumvalue of the image impedance W of the coupling circuit, is chosen asapproximately equal to the terminating resistances R- which are equal inthis case. C is the effective shunt capacity across the primary orsecondary winding including the effective distributed capacity of thesewindings. f and f are respectively the lower and upper limitingfrequencies. is is the coefiicient of coupling. 7, is the resonantfrequency. L is the primary inductance. W. is the image impedance of thecoupling circuit to which the primary winding of the receiving coil isconnected and is equal to the secondary inductance. W, is the minimumvalue of From equation 1) it will be found that is approximately equalto .975 where f is to have a value of 35 kilocycles and f is value of 4kilocycles. It is impossible to I00 rangement as obtain this value of kwith the winding aremployed in the prior art on air core coils. However,by winding the repeating coil in accordance with one of the embodimentsof the invention as described below, this value of 76 can be obtained.In winding'the repeating coil, the first part is applied as a quad (twoprimary and two secondary windings twisted together) which is appliedwith approximately equal turns in each section'of a two-section spool.The two primary windings and the two secondary windings each consistingof a twisted pair, are then separated, the two primary windings beingapplied over the quadded section-in one section of the spool,while thetwo secondary windings are applied over the quadded section in the othersection of the spool. This results in an arrangement in which part ofthe primary winding is closely coupled with the secondary in the quaddedsection and loosely coupled in the outer section. By properly'proportioning the number of turns in the quadded and outer sections ofthe windings, a wide variation in the leakage inductance or couplingfactors can be obtained for a predetermined value of self-impedance ofthe individual windings to satisfy equation -(1) above. Externalcondensers may be added when required across the primary and secondarywindings so that their value plus the effective shunt capacity of thewindings will satisfy equa tion (5) above- With winding arrangementssuch as described above, it is impossible to electrostatically shieldthe primary windings from the secondary windings by the usual methodsemployed in the prior art. However, in accordance with anotherembodiment of the invention it is possible to construct a repeating coilhaving a high coupling coefficient, and at the same time windingelectrostatically shielded from the secondary winding. This isaccomplished by employing a shielded conductor, or a twisted pair ofwires enclosed in a shield, and twisting the shielded conductor orconductors with the conductor or conductors which form the secondarywindings, before applying the windings to thespool." Preferably theshield is grounded at the midpoint of the windings. The longitudinalcurrent flowing from the circuit to which the shieldedwinding isconnected to ground will pass from the shielded winding to the shieldand as the flux created by the current flowing in the shield will beopposite in the two halves of the shield, the resultant impedance to theflow of these currents through theshield can be'made very small.However, only .longi-I t'udinal' current will flowthrough the shieldsurrounding the conductors as the shield will assumepractically the samepotential as the sentation .of the having its primary.

winding which a shields all along its length with respect to thetransmitted voltage.

The invention will be better understood by reference to the followingdetailed description and accompanying drawings in which:

Fig. l is a conventional schematic representation of a coupling circuitin which the invention may be embodied;

Fig. 2 is a cross-sectional view of a repeating'coil showing the methodof applying the windings over the core in accordance with one embodimentofthe invention;

Fig. 3 is a'conventional schematic representation of therepeating coilshown in Fig. 2; p

r Fig. 4 is a cross-sectional view of a repeating coil showing themethod of applying'the with windings over the core in accordance anotherembodiment of the invention;

Fig; 5 is'a conventionalschematic repre repeatlng coil shown in Fig.4;

Fig. 6 is a cross-sectional view of a repeating coil showing themethodof applying the winding over the core in accordance with stillanother embodiment of the invention; and

Fig. -7 is a conventional schematic representation of therepeating coilshown in Fig.6.

Referring to Fig. '1: the coupling circuit comprises an anti-resonantcircuit 11 con-' nected through equal impedances 12 to a source ofvarlable voltage 13' and a second anti-resonant circuit 14 inductivelycoupled to circuitll and connected to an output impedance 15. Circuits11 and 14 preferably comprise the primary and secondary windingsrespectively of an air core repeating coil as shown in Figs. 2 and 3 andare preferably proportioned to resonate at substantially the sameresonant'frequency. The primary and secondary windings are'preferablyelect-rostatically shielded from' each other by a grounded shield S towhich shield one end of the secondary winding is preferably connected.NVhen the electrostatic shield S is not used the midpoint6, 1 of theprimary winding is preferably grounded. The coeiiicicnts'of capacityelements in the anti-resonant circuits 11 and 14 are C and C respectively, and the inductances are L and L respectively. C; and C arepreferably made equal to-each other and preferably comprise theeffective shunt capacity across the pri mary winding 5, 6, 1, 2 andsecondary winding 7, 8, 3, 4 respectively, although individualcapacities maybe added when required across the primary and secondarywindings to obtain the proper value of capacity. The inductances L and Lof the primary and sec onda'ry. windings are preferably made equal toeach other and'the sum of the two impedances 12 is equal to impedance15. g i-The air core repeating coil shown in Figs. Q'and 3 preferablycomprises a spool 16 having a central partition 17 forming spoolsections 18 and 19. A primary winding 5, 5A, 5B, 6, 1, 1-B, 1 A, 2 and asecondary winding 7, 7B, 7-A, 8, 3, 3-13, 3-A, 4 are applied over thespool. The primary winding is preferably made up of four sections 5,5-A; 5B, 6; 1, 1B; and 1A, 2, with the terminals 5- connected to 5-B, 6connected to 1 and 1B connected to 1-A so that the sections areconnected in series aiding relation. The secondary winding is preferablymade up of four sections 7, 7A; 7B, 8; 3, 3B; and 3-A, 4, with theterminals 7-A connected to 7B, 8 connected to 3 and 3B connected to 3Aso that the sections are connected in a series aiding relation. Theconductors forming the sections 5, 5A and 1A, 2 of the primary windingand those orming the sections 7, 7-13 and 3A, 4 of the secondary windingare preferably twisted One-half of the conductors in each spooltogether. The conductors forming the sections 5B, 6 and 1, l-B of theprimary winding are preferably twisted together to form a pair and woundin section 18 over the quadded winding. The conductors forming thesections 7B, 8 and 3, 3-B of the secondary winding are preferablytwisted together to form a pair and wound in the section 19 over thequadded winding.

The individual conductors forming the sections 5, 5-A and 1-A, 2 arepreferably surrounded by individual electrostatic shields S concentricwith the conductors, which shields ied before the conductors are formedThe ends of the shields S are connected together adjacent theconnections of the terminals of the concentric conductors therein asshown in Fig. 3. The sections 5B, 6 1, 1-B of the primary winding arepreferably enclosed in an electrostatic shield 20, which shield 20 isconnected to the electrostatic shields S as shown in Fig. 3.

If desired the conductors forming the seesection connected with thetwisted pair.

hen it is unnecessary to have the primary and secondary windingselectrostatically shielded from each other, concentric shields S and theshield 20 may be omitted.

In a specific embodiment of the invention constructed the conductorsforming the winding sections 5, 5A; 1-A, 2; 7, 7B and 3-A, 4 were formedin a quad and 190 turns of the quadded conductors were applied in eachspool section, the conductors forming the winding sections 5B, 6 andwere formed in a pair and 60 turns of the paired winding were appliedover the quadded winding in one spool section and the conductors formingthe winding sections 7-A, 8 and 3, 3-B were formed in a pair and 60turns of the paired winding were applied over the quadded winding in theother spool section. The individual sections of the primary winding andthe individual sections of the secondary winding were connected togetherin a series aiding relation.

Each of the individual conductors comprised No. 24 double cotton coveredcopper wire. No individual electrostatic shields concentric with theconductors were employed in this particular embodiment. The spool wasformed from wood, the core being circular and having a diameter of 2inches. Each of the two spool sections was '7 inch wide and 1% inchesdeep. The central partition between the two spool sections was inchwide.

Tests made on this coil showed a transmission loss over a range offrequencies from 5KC to 30KC of less than one decibel and a variation intransmission loss of less than one-half decibel. The reflectioncoefiicient over the same frequency range was less than 20%.

In Fig. 3 the inherent capacities existing between the sections of theprimary and secondary windings and between the shields S and 20 and thewindings are shown. These capacities between the individual sections ofthe secondary respect to the center and ends of the winding; thecapacities between the individual sections of the primary winding aresymmetrical with respect to the center and ends of the winding; and thecapacities between the shield sections S and 20 and the primary andsecondar windings are symmetrical to the shield 20 at the groundconnection thereto.

The longitudinal currents flowing from the source 13 through the twobalanced impedances 12, to which the shielded primary winds ing 5, 6, 1,2 is connected will flow from this winding to the shields S and 20 andto ground andv as the fluxes created by the currents flowing in theshields S will be substantially equal and opposite in the two sections18 and 19 of the spool. 16, the resultant impedance through the shieldsS to this long current is very small. This substantially eliminatesstray circulating currents in the secondary winding due to longitudinalcurrent present in the primary side of the circuit. As the shieldsections S will have the same potential as the concentric conductors ofthe primary winding therein, only longitudinal currents will flow thehollow conductor shields S.

The midpoint 6, 1 of the primary winding may be grounded when theprimary winding of the repeating coil is connected to a balanced circuitby the connection 21.

winding are symmetrical with M through CID at the outer ends of thewindings By varyin the number of turns in the sections 5, 5- ,and 1A, 2of the primary winding the number of turns in the sections 7, 7 -B and3A, l of the secondary winding, which sections are wound as a quad, withrespect to the number of turns in the sections 5B, 6 and 1, 1B of theprimary winding and the number of turns in the sections 7 13, 8 and 3,3-B of the secondary winding, a large variation in the couplingcoefficient may be obtained.

The repeating coil shown in Figs. 1 and 5 comprises a primary winding55, 56, 51-, 52 and a secondary winding 57, 58, 53, 5 1 wound on a spool16 having a central partition 17 to form spool sections 18' and 19. Eachof the sections 55, 56 .and 51, '52 of the primary winding is preferablyenclosed in an individual electrostatic shield S which is concentricwith the conductor forming the individual section. The section of thesecondarywinding 57, 58 and the section of the primary winding, 55, 56with its concentric shield are preferably twisted together and wound inthe spool section 18 and the section 51, 52 of, the primary winding withits concentric shield and the section 53, 54; of the secondary windingare preferably twisted together and wound in the spool section 19 in anopposite direction to that of the winding in the spool section 18. Theouter terminals of the winding sections are connected toether as shownand the ends of the conceni ric shields S surrounding the primary windmgare connected together and to ground spool sections 18 and 19. i

This construction provides a high degree of coupling, especially in thecase of an air core coil and also prevents noise or longitudinalcurrents from passing from the primary winding to the secondary winding.

The repeating coil shown in Figs. 6 and 7 comprises a spool 16 having apartition17 forming spool sections 18 and 19, a primary winding7 5, 76,71, 72 and a secondary winding77, 77B, 77A. 78, 73, 73-B, 78--A., 7 4:.Each of the winding sections 5, 7 6 and 71, 7 2 of the primary windingis preferably enclosed in an individual electrostatic shield S which isconcentric with the conductor forming the individual winding section.Seetions 71. 72 of the primary winding and 7 8, 73B of the secondarywinding are preferably twisted together and wound in the spool section19. Sections 75. 76 and 77A. 78 of the secondary winding are preferablytwisted together and wound in the spool seetion18 in an oppositedirection to that of the winding inspool section 19. The inner ter-,

minals 71 and 76 of the primary winding sections are connected togetherterminals 7 3 and 78 of the secondary winding sections are connectedtogetheras shown. The shield sections S are connected togetherin the twoand the inner and to ground adjacent the terminals 76 and" 71. Each ofthe winding sections 73 A, 7 4L and 7 7 7 7B of the secondary windingcomprises a relatively few turns which are the coupling coefficient toobtain uniform transmission over a range of frequencies and a lowreflection coefficient. The winding section 72 -A, 74: ispreferablywound in spool section 18 over the twisted pairof windings and employedto adjust to the desired value the winding section 77, 77B is preferablywound in the spool section 19 over the twisted pair. These w ndingsections 7 3A,7 a and t! r7-B are connected in a series aiding re-:

lation to the secondary winding sections 7 3, 78B and 7877-A as shown.

. When it is unnecessary to electrostatically invention have been shownand described in deta l it isto be understood that the invention isgeneric in ch araeter and is not to be limitedto the particularembodiments since numerous modifications thereof may be made by personsskilled in the art without departing from the sp rit of applicantsinvention, the scope of which is to be determined by the appendedclaims.

, What is claimed is:

1. An inductive device comprising a spool and two primary and twosecondary windings thereon, said windings being applied to said spoolpartly as a quad comprising turns 7 of both primary and secondarywindings and partlyas individual twisted pair primary turns and twistedpair secondary turns.

2. An inductance device comprising a plurality of conductors twistedtogether to form a-unitary cord, and means for reducing the directelectrostatic capacity between one of said conductors and at least oneother of said conductors, said means comprising a hollow conductorconcentric with and insulated from sail one conductor toelectrostatically shield said one conductor from the other of saidconductors. v

3. A repeating coil comprising a non-magnetic spool having two windingsections and two primary and two secondary windings thereon, saidwindings being applied partly as a quad with approximately an equalnumberof turns in each winding section and partly as individual twistedpair primary and secondarywindin gs with the twisted p air primarywinding portion wound in one of said winding sections over the quaddedwinding portion and the twisted pair secondary winding portion wound inthe other of said ice winding port-ion.

4. A repeating coil comprising a spool and at least one primary and onesecondary winding thereon, said primary and secondary windings beingapplied partially as a unitary cord formed of twisted conductors andpartially with said primary and secondary windings as individual unitsseparated from each other.

5. An inductance sections over said quadded winding device comprisingprimary and secondary windings, each of said windings comprising aplurality of sections, the conductor or conductors of at least one ofsaid sections of said primary winding being twisted together with theconductor or conductors of at least one of said sections of saidsecondary winding, and means to electrostatically shield at least one ofsaid twisted primary and secondary sections from each other, said meanscomprising an electrostatic shield coaxial to and surrounding one ofsaid conductors.

6. A repeating coil comprising a spool and at least one primary and onesecondary winding thereon, said primary and secondary windings beingapplied partially as a unitary cord formed of twisted conductors andpartially with said primary and secondary windings separated from eachother, and means to electrostatically shield at least a portion of theconductor forming one of said windings from a portion of the conductorforming the other of said windings, said means including a coaxialshield surrounding the portion of said one conductor which is applied asa unitary cord with said portion of said other conductor.

7. An inductance device having a band frequency characteristiccomprising a spool and at least one primary and one secondary windingthereon, part of said primary and secondary windings being applied as aunitary cord in a manner such that a low leakage inductance between thewindings is obtained and another part of said windings being applied asindividual primary and secondary conductors so that a high leakageinductance between said windings is obtained.

In witness whereof, I hereunto subscribe my name this 26th day of June,1931.

ARTHUR J. CHRISTOPHER.

